1. Field of the Invention
The present invention relates to a vibration wave driven motor and, more particularly, to a vibration wave driven motor of a type in which an elastic member along which a travelling wave is generated is kept in tight contact with a rail-like stator, and the elastic member is moved along the rail-like stator, and a printing apparatus using this vibration wave driven motor.
2. Related Background Art
A conventional vibration wave driven motor of this type is shown in FIGS. 11 and 12.
An elastic member 1 consists of a metal material and has a projection 1a on a sliding surface side. An AC voltage is applied to piezoelectric elements 2 bonded to the upper surface of the elastic member 1 to generate a travelling vibration wave therein. The principle of generating the travelling vibration wave and the structure of the piezoelectric elements 2 are known, and a detailed description thereof will be omitted. AC voltages having a 90.degree. phase difference in time are applied to two drive piezoelectric element groups spaced apart from each other at an angular interval of 90.degree., thereby generating a travelling vibration wave. A rail-like stator 8 is in frictional contact with the elastic member 1 and is fixed on a bottom plate 9 of a motor case. The rail-like stator 8 is kept in contact with the elastic member 1 through a vibration insulating material 5 (e.g., a felt) by a pressure spring 3.
A plate-like auxiliary support 6 is bonded to a projection 1b formed at one linear portion of the elastic member 1 and supports a table 4, so that the elastic member 1 can linearly move smoothly together with the table 4 without cluttering. The contact width between the elastic member 1 and the rail-like stator 8 is set large to reduce the rigidness of the plate-like auxiliary support 6. Hence, the elastic member 1 conforms to the frictional surface of the rail-like stator, thereby stably moving the elastic member 1.
The rail-like stator 8 has a flange 8a to softly receive the vibration of the elastic member 1. That is, the rail-like stator 8 has spring properties.
This motor is used for driving a printing head in a printer of, e.g., a bubble jet scheme. The printing head is mounted on a carriage (not shown) mounted on the table 4 to linearly reciprocate the printing head.
The amplitude of the vibration of the elastic member 1 in a Z direction is large in its outer peripheral portion in the conventional example and small in its inner peripheral portion, as shown in FIG. 13. To the contrary, the vibrations at the flange 8a of the rail-like stator 8 have amplitudes opposite to those of the elastic member 1. As shown in FIG. 13, when the elastic member is set in a state 100, the flange 8a is set in a state 800a. Only the outer peripheral portion (edge) of the elastic member is in contact with the flange. In this state, the contact width is small, and a stable contact state cannot be obtained. In some cases, the distal end of the flange is brought into contact with or separated from the inner periphery of the elastic member 1 to generate noise. In addition, the contact portion is the proximal portion of the flange, and the spring properties of the flange cannot be sufficiently exhibited. As a result, the vibrations of the elastic member cannot be received softly and noise is generated.
Even if the elastic member is in contact with the flange 8a from the outer to inner peripheries, the contact state between the elastic member and the flange 8a is not always uniform, and the sliding loss is large, thereby decreasing the feed velocity of the table 4.
If the above adverse influences are to be eliminated by reducing the contact width between the elastic member 1 and the flange 8a of the rail-like stator 8, as shown in FIG. 14, the position of the elastic member 1 in a B.sub.Z direction becomes unstable because in dimensional errors of each of the parts. As a result, stable feeding cannot be performed.